The invention concerns the treatment of fibres and is concerned with a method for making rods of bonded fibrillated polyolefin, preferably polypropylene, particularly for use as or in tobacco-smoke filters.
To improve the firmness of tobacco-smoke filter rod composed of a tow of crimped continuous or fibrillated filaments of polyolefin, it is known to use a polymeric bonding agent. The non-volatile liquid organic plasticizers which are effective bonding agents for crimping cellulose-acetate tow cannot be used for bonding polyolefins, as they do not soften polyolefin fibres. Polyolefin tow can be bonded by mixing with another polyolefin, particularly polyethylene, and heating the rod to effect fusion. The bonding agent, for example polyethylene, may be incorporated during the melt-spinning operation. Polyolefin tow may alternatively be bonded by using a spray of, for example, a polymerizable unsaturated organic ester such as vinylacetate, an acrylate ester or a vinyl ether. Generally the rod is heated to effect curing.